Question

I’m developing an XSLT 1.0 stylesheet (and apply it using xsltproc). One of the templates in my script should perform some special handling for the first <sect1> element in a given parent node and some for the last <sect1> element. Right now this special handling is implemented like this:

<xsl:template match="sect1">
  <xsl:if test="not(preceding-sibling::sect1)">
    <!-- Special handling for first sect1 element goes here. -->
  </xsl:if>
  <!-- Common handling for all sect1 elements goes here. -->
  <xsl:if test="not(following-sibling::sect1)">
    <!-- Special handling for last sect1 element goes here. -->
  </xsl:if>
</xsl:template>

I was wondering (just out of curiousity, the runtime speed of the script is fine for me): is there a more efficient way to do this? Is it likely that the XSLT processor will stop assembling the preceding-sibling::sect1 node-set after the first found match because it knows that it just needs to find one or zero elements?

Answer 1

Is it likely that the XSLT processor
will stop assembling the
preceding-sibling::sect1 node-set
after the first found match because it
knows that it just needs to find one
or zero elements?

I don’t know about xsltproc, but Saxon is very good at these sorts of optimizations. I believe it would only check for the first found match because it only needs to know whether the node-set is empty or not.

However you could always make sure by changing your tests as follows:

  <xsl:if test="not(preceding-sibling::sect1[1])">

and

  <xsl:if test="not(following-sibling::sect1[1])">

as this will only test for the first sibling along each axis. Note that the [1] in each case refers to the order of the XPath step, which is the order of the axis, not necessarily document order. So preceding-sibling::sect1[1] refers to the sect1 sibling immediately preceding the current element, not the first sect1 sibling in document order. Because the direction of the preceding-sibling axis is reverse.